This invention relates to a heating and cooling system for environmental spaces and domestic hot water, and more particularly to a system which utilizes a heat exchange material which undergoes reversible phase changes during operation to store and release energy.
Due to the present concern over rapidly increasing costs of conventional energy forms, many systems have been developed to conserve the more expensive energy sources by utilizing heat from cheaper energy sources such as solar or geothermal heat. Heat stored by these systems is then used for domestic or commercial heating of buildings and water. Similar systems which store energy at relatively low temperatures have been developed for cooling buildings.
One example of a system which provides both heating and cooling through the use of hot and cold storage tanks is Thomason et al, U.S. Pat. No. 3,980,130. Thomason teaches the use of a heat transfer fluid such as water which accepts heat from a source of supply, such as a solar collector or an air conditioner compressor. Then, through a series of pumps and conduits, is transferred to either the hot or cold storage tank. This is accomplished by either directly dumping fluid into the tanks or by using a heat transfer coil to transfer heat from the operating liquid to the liquid stored in the tanks.
Various methods have been proposed for then removing the heat stored in the tanks to heat or cool a building. For example, in the above-mentioned '130 patent, the storage tanks are in heat transfer relationship with stones through which air is passed. The air is heated (or cooled as the case may be) by the stones and is then circulated through the air handling or ventilation system for the building. An alternative method which has also been used in the art is transferring heat through a separate set of coils extending into a storage tank with a separate heat transfer fluid therein. After picking up heat from the storage tank, the fluid is circulated through radiator-type coils positioned either in an air handling system or radiating directly to the interior of a building.
Another example of a heating and cooling system utilizing storage tanks is Camp, U.S. Pat. No. 4,169,554. Camp teaches a system which includes two storage tanks, one containing a material such as a wax that undergoes a phase change at 100.degree.-140.degree. F. and the other containing water. Solar collectors supply, via heat exchange coils, heat to the wax-containing tank which stores the heat until needed. Solar energy is also used to heat the water in the other tank for storage until needed. A conventional heat pump provides back-up heating when required.
The Camp system operates in a cooling mode by using a refrigeration cycle to chill the water in the second storage tank and form an ice mass during off-peak hours. That ice mass is then used to provide comfort cooling during peak hours. A conventional heat pump in the cooling mode provides back-up cooling when required. However, the system has only a limited storage capability and relies on the use of relatively expensive energy in the form of electricity to operate a compressor to form the ice mass.
An example of a heating and cooling system using an ice storage tank in an annual cycle energy system (ACES) is illustrated by the article "Ice Block House", Popular Science (February 1977). That article describes a system having a storage tank 20 feet by 20 feet by 4 feet deep in which water is frozen by drawing heat from it during the winter months for comfort heating and then is thawed during the summer months for comfort cooling. Energy costs are taught to be reduced substantially over a conventional heating and cooling system. The system takes advantage of the latent heat of fusion of water as well as sensible heat effects to reduce the overall size of the storage tank which is required. However, the system loses efficiency because it requires an antifreeze solution loop inside the storage tank in heat exchange relation to a refrigerant loop outside the storage tank to draw and use heat from the water/ice mixture in the storage tank. Another, one of the problems with the disclosed system is the buildup of ice on the antifreeze solution containing coils in the storage tank. As ice builds up, the rate of heat transfer to the antifreeze solution decreases and makes the system less efficient, thus requiring the use of defrost cycles and a specially constructed antifreeze solution loop in an attempt to shed the ice which forms.
Accordingly, the need still exists in the art for an efficient heating and cooling system for environmental spaces and domestic hot water which makes maximum utilization of energy sources.